From 6e29836f794abdd91aa03d334b72b7a7f4800e92 Mon Sep 17 00:00:00 2001

From: Greg Hudson <ghudson@mit.edu>

Date: Sat, 4 Aug 2018 23:55:18 -0400

Subject: [PATCH] Use a hash table for MEMORY ccache resolution

In cc_memory.c, replace the linked list of caches with a hash table,

for better performance with large numbers of memory caches.

ticket: 8722 (new)

(cherry picked from commit 088ba228acce4fd55bbb7c30122fe2703b8beeb8)

---

 src/lib/krb5/ccache/cc_memory.c | 77 +++++++++++++++------------------

 1 file changed, 34 insertions(+), 43 deletions(-)

diff --git a/src/lib/krb5/ccache/cc_memory.c b/src/lib/krb5/ccache/cc_memory.c

index cfd5c6389..114ef6913 100644

--- a/src/lib/krb5/ccache/cc_memory.c

+++ b/src/lib/krb5/ccache/cc_memory.c

@@ -26,6 +26,7 @@

 #include "cc-int.h"

 #include "../krb/int-proto.h"

+#include "k5-hashtab.h"

 #include <errno.h>

 static krb5_error_code KRB5_CALLCONV krb5_mcc_close

@@ -118,12 +119,6 @@ typedef struct _krb5_mcc_data {

     int generation;             /* Incremented at each initialize */

 } krb5_mcc_data;

-/* List of memory caches.  */

-typedef struct krb5_mcc_list_node {

-    struct krb5_mcc_list_node *next;

-    krb5_mcc_data *cache;

-} krb5_mcc_list_node;

-

 /* Iterator over credentials in a memory cache. */

 struct mcc_cursor {

     int generation;

@@ -136,10 +131,27 @@ struct krb5_mcc_ptcursor_data {

 };

 k5_cc_mutex krb5int_mcc_mutex = K5_CC_MUTEX_PARTIAL_INITIALIZER;

-static krb5_mcc_list_node *mcc_head = 0;

+static struct k5_hashtab *mcc_hashtab = NULL;

 static void update_mcc_change_time(krb5_mcc_data *);

+/* Ensure that mcc_hashtab is initialized.  Call with krb5int_mcc_mutex

+ * locked. */

+static krb5_error_code

+init_table(krb5_context context)

+{

+    krb5_error_code ret;

+    uint8_t seed[K5_HASH_SEED_LEN];

+    krb5_data d = make_data(seed, sizeof(seed));

+

+    if (mcc_hashtab != NULL)

+        return 0;

+    ret = krb5_c_random_make_octets(context, &d);

+    if (ret)

+        return ret;

+    return k5_hashtab_create(seed, 64, &mcc_hashtab);

+}

+

 /* Remove creds from d, invalidate any existing cursors, and unset the client

  * principal.  The caller is responsible for locking. */

 static void

@@ -230,21 +242,13 @@ krb5_mcc_close(krb5_context context, krb5_ccache id)

 krb5_error_code KRB5_CALLCONV

 krb5_mcc_destroy(krb5_context context, krb5_ccache id)

 {

-    krb5_mcc_list_node **curr, *node;

     krb5_mcc_data *d = id->data;

     krb5_boolean removed_from_table = FALSE;

+    /* Remove this node from the table if it is still present. */

     k5_cc_mutex_lock(context, &krb5int_mcc_mutex);

-

-    for (curr = &mcc_head; *curr; curr = &(*curr)->next) {

-        if ((*curr)->cache == d) {

-            node = *curr;

-            *curr = node->next;

-            free(node);

-            removed_from_table = TRUE;

-            break;

-        }

-    }

+    if (k5_hashtab_remove(mcc_hashtab, d->name, strlen(d->name)))

+        removed_from_table = TRUE;

     k5_cc_mutex_unlock(context, &krb5int_mcc_mutex);

     /* Empty the cache and remove the reference for the table slot.  There will

@@ -289,16 +293,13 @@ krb5_mcc_resolve (krb5_context context, krb5_ccache *id, const char *residual)

 {

     krb5_os_context os_ctx = &context->os_context;

     krb5_ccache lid;

-    krb5_mcc_list_node *ptr;

     krb5_error_code err;

     krb5_mcc_data *d;

     k5_cc_mutex_lock(context, &krb5int_mcc_mutex);

-    for (ptr = mcc_head; ptr; ptr=ptr->next)

-        if (!strcmp(ptr->cache->name, residual))

-            break;

-    if (ptr != NULL) {

-        d = ptr->cache;

+    init_table(context);

+    d = k5_hashtab_get(mcc_hashtab, residual, strlen(residual));

+    if (d != NULL) {

         k5_cc_mutex_lock(context, &d->lock);

         d->refcount++;

         k5_cc_mutex_unlock(context, &d->lock);

@@ -438,18 +439,17 @@ krb5_mcc_end_seq_get(krb5_context context, krb5_ccache id, krb5_cc_cursor *curso

 }

 /*

- * Utility routine: Creates the back-end data for a memory cache, and threads

- * it into the global linked list.  Give the new object two references, one for

- * the table slot and one for the caller's handle.

+ * Utility routine: Creates the back-end data for a memory cache, and adds it

+ * to the global table.  Give the new object two references, one for the table

+ * slot and one for the caller's handle.

  *

- * Call with the global list lock held.

+ * Call with the global table lock held.

  */

 static krb5_error_code

 new_mcc_data (const char *name, krb5_mcc_data **dataptr)

 {

     krb5_error_code err;

     krb5_mcc_data *d;

-    krb5_mcc_list_node *n;

     d = malloc(sizeof(krb5_mcc_data));

     if (d == NULL)

@@ -476,18 +476,13 @@ new_mcc_data (const char *name, krb5_mcc_data **dataptr)

     d->generation = 0;

     update_mcc_change_time(d);

-    n = malloc(sizeof(krb5_mcc_list_node));

-    if (n == NULL) {

+    if (k5_hashtab_add(mcc_hashtab, d->name, strlen(d->name), d) != 0) {

         free(d->name);

         k5_cc_mutex_destroy(&d->lock);

         free(d);

         return KRB5_CC_NOMEM;

     }

-    n->cache = d;

-    n->next = mcc_head;

-    mcc_head = n;

-

     *dataptr = d;

     return 0;

 }

@@ -522,11 +517,10 @@ krb5_mcc_generate_new (krb5_context context, krb5_ccache *id)

     lid->ops = &krb5_mcc_ops;

     k5_cc_mutex_lock(context, &krb5int_mcc_mutex);

+    init_table(context);

     /* Check for uniqueness with mutex locked to avoid race conditions */

     while (1) {

-        krb5_mcc_list_node *ptr;

-

         err = krb5int_random_string (context, uniquename, sizeof (uniquename));

         if (err) {

             k5_cc_mutex_unlock(context, &krb5int_mcc_mutex);

@@ -534,12 +528,9 @@ krb5_mcc_generate_new (krb5_context context, krb5_ccache *id)

             return err;

         }

-        for (ptr = mcc_head; ptr; ptr=ptr->next) {

-            if (!strcmp(ptr->cache->name, uniquename)) {

-                break;  /* got a match, loop again */

-            }

-        }

-        if (!ptr) break; /* got to the end without finding a match */

+        if (k5_hashtab_get(mcc_hashtab, uniquename,

+                           strlen(uniquename)) == NULL)

+            break;

     }

     err = new_mcc_data(uniquename, &d);